Human papillomaviruses (HPVs) of the high-risk types induce hyperproliferative lesions in epithelial tissues and are etiologic agents for cancers of the genital cervix and oral cavity. The E6 and E7 oncoproteins encoded by the high-risk HPVs are believed to play central roles in the development of the HPV-related malignancies. The goal of this proposal is to elucidate the mechanisms by which the E7 oncoprotein modifies functions of the host cell regulators. The proposal stems from the observation that E7 specifically induces the proteolytic degradation of the tumor suppressor Rb. Moreover, inhibitors of 26S proteasome inhibit E7- induced degradation of Rb. A main objective of the proposal is to determine the basis of the specificity and analyze the mechanism by which E7 causes proteolysis of Rb. By regulating Rb, E7 increases the transcriptional activity of the E2F-family of transcription factors (E2Fs). Interestingly, E7 also increases the activity of the DNA repair protein DDB that functions as a transcriptional coactivator of E2Fs. DDB possesses homology with the Cockayne syndrome protein GS-A, which is involved in transcription-coupled repair (TCR). The proposal focuses on the role of the E7 mediated increase in DDB in the activation of E2Fs as well as in DNA repair. The hypothesis that E7, by increasing the activity of DDB, stimulates TCR of the E2F-regulated replication genes will be investigated. These studies on the repair function of E7 will provide insights into the mechanisms of drug resistance in cervical cancer patients. The specific aims are: 1. What is the basis of specificity of Rb-degradation by E7? 2. What is the mechanism by which E7 causes proteolysis of Rb? 3. Does E7 play a role in transcription-coupled repair of the E2F- regulated replication genes?